Abstract: In order to discuss the propagation and amplification characteristics of ultrashort optical pulse in distributed fiber amplifiers and the influencing factors,its basic propagation equation was established.Taking an ytterbium-doped fiber amplifier as example,the evolution of optical pulse in the amplifier was simulated by means of split-step Fourier transform method.Then the effect of initial chirp and gain dispersion were discussed.The results show that when the optical pulse propagates in a distributed optical fiber amplifier,dispersion and nonlinear effect of the fiber will affect pulse profile and frequency spectrum, and initial chirp also influence the propagation state of optical pulse.For wide-spectrum optical pulse,gain dispersion is equivalent to a loss mechanism,so its influence should be considered.Relevant results have certain reference value to the system design and optimization of optical fiber amplifiers.